Evacuations ordered after increase in activity from Mount Ibu on Halmahera Island, Indonesia.

Authorities in North Maluku Province, Indonesia, have ordered the evacuation of six villages close to Mount Ibu, a 1325 m stratovolcano on the northwest coast of Halmahera Island, following a series of eruptions in the first two weeks of 2025. Mount Ibu began its current eruptive cycle in June 2024, but January has seen a significant rise in activity, with more than a thousand eruptions have been recorded on the volcano this year, with the largest producing ash columns reaching as high as 4 km over the summit of the volcano. However, to date only one village, with a population of 517 people, has been evacuated, with about 2500 people in the remaining five villages reluctant to leave without first harvesting crops.

An eruption on Mount Ibu, Halmahera Island, on Wednesday 15 January 2024. Azzam/AFP.

The Halmahera Island chain is a volcanic arc formed where the Halmahera Plate, a northeaster extension of the Molucca Sea Plate is being subducted beneath Philippine Plate from the east and the Eurasian Plate from the west, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

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Exclusion area around Mount Ibu, Halmahera Island, extended following new eruption.

The Indonesian Center for Volcanology and Geological Hazard Mitigation has extended the exclusion zone around  Mount Ibu, a 1325 m stratovolcano on the northwest coast of Halmahera Island, following a new eruption on 18 May 2024. A two kilometre exclusion zone had already been put in place after the volcano began erupting on 28 April, but this has been increased to seven kilometres following the most recent eruption, which produced an ash column which rose to 4 km above the volcano's summit, resulting in seven villages needing to be evacuated. 

An ash column and lava fountain above Mount Ibu on the Indonesian island of Halmahera on 18 May 2024. Several lightning discharges can be seen within the ash column; ash columns can build up considerable charge variations leading to frequent electrical discharges. Indonesian Center for Volcanology and Geological Hazard Mitigation/Reuters.

The Halmahera Island chain is a volcanic arc formed where the Halmahera Plate, a northeaster extension of the Molucca Sea Plate is being subducted beneath Philippine Plate from the east and the Eurasian Plate from the west, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

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Eruption on Mount Ibu, Halmahera Island, Indonesia.

The Regional Disaster Mitigation Agency for West Halmahera District has reported an eruption on Mount Ibu, a 1325 m stratovolcano on the northwest coast of Halmahera Island, Indonesia, on Sunday 28 April  2024 (a stratovolcano is a cone-shaped volcano made up of layers of ash and lava, although Mount Ibu has a truncated shape, having lost its upper part in an explosion at some point in the past). The eruption started at 0.37 am local time, and lasted approximately three minutes and 26 seconds, producing a column of dark ash which rose 3.5 km above the summit of the volcano and drifted to the west. The Regional Disaster Mitigation Agency has asked people not to go within 2 km of the volcano for the time being, and has issued dust masks to residents of 16 villages in the area. Sam Ratulangi International Airport, about 100 km from the volcano in the city of Manado, is closed to flights temporarily.

An ash column over Mount Ibu at 0.44 am local time on Sunday 28 April 2024. Abdul Fatah/Antara News Agency.

The Halmahera Island chain is a volcanic arc formed where the Halmahera Plate, a northeaster extension of the Molucca Sea Plate is being subducted beneath Philippine Plate from the east and the Eurasian Plate from the west, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

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Alionchis jailoloensis: A new species of Onchidiid Slug from the Mangroves of Halmahera, eastern Indonesia.

Onchidiid Slugs are shell-less Gastropods found almost exclusively in Mangroves and intertidal zones (though two species are found at high altitudes in Montane Rianforests in Borneo and the Philippines). Remarkably, unlike all other marine Gastropods, they are air-breathing Pulmonates, closely related to terrestrial Slugs and Snails, and cannot survive below the low-tide line, as if they are not periodically exposed to the air they will drown. Onchidiids reach their maximum diversity in Southeast Asia and Indonesia, but are found around the world, reaching as far north as Scotland and Alaska.

In a paper published in the journal Raffles Bulletin of Zoology on 21 May 2018, Tricia Goulding of the Department of Biology at Pennsylvania State University, and the Bernice Pauahi Bishop Museum, Munawar Khalil of the Department of Marine Science at Universitas Malikussaleh, Shau Hwai Tan of the Marine Science Laboratory and Centre for Marine and Coastal Studies at Universiti Sains Malaysia, and Benoît Dayrat, also of the Department of Biology at Pennsylvania State University, describe a new species of Onchidiid Slug from Halmahera Island in Indonesia.

The new species is named Alionchis jailoloensis, where 'Alionchis' honours Ali, an assistant of Alfred Russel Wallace during his travels in the Malay Archipelago, originally hired as a cook, but who went on to make a significant contribution to the study of Ornithology in the region, and 'jailoloensis' means 'from Jailolo', a small port on Halmahera, near where the species was discovered, and the  former name of the entire island. Alionchis jailoloensis is flattened with thick eyestalks and additional eyes on its dorsal surface, it is muddy brown in colour and reaches about 65 mm in length. 

Live specimens, Alionchis jailoloensis, Indonesia, Halmahera. (A) Dorsal view, 63 mm long; (B) Dorsal view, 48 mm long; (C) Dorsal view, holotype, 43 mm long); (D) Dorsal view, 64 mm long; (E) Dorsal view (the arrow points to the pneumostome), same as (A); (F) Dorsal view, 51 mm long); (G) Dorsal view, 61 mm long; (H) Lateral view, 69 mm long; (I) Ventral view, 33 mm long; (J) Ventral view, 45 mm long. Goulding et al. (2018).

Alionchis jailoloensis was found living on mudflats between trees in open Mangrove Forest. It appears to be endemic to the island of Halmahera (i.e. not found anywhere else), which is unusual for a Onchidiid Slug, as most species have quite wide distributions.

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Magnitude 5.9 Earthquake beneath Posi Posi Rao Island, North Maluku Province, Indonesia.

The United States Geological Survey recorded a Magnitude 5.9 Earthquake at a depth of 20.3km, beneath the northern part of Posi Posi Rao Island in the North Maluku Province of Indonesia, slightly slightly after 1.05 am local time on Sunday 19 November 2017 (slightly after 4.05 pm on Saturday 18 November, GMT). There are no reports of any casualties associated with this event, but it did cause some minor damage to buildings in Posiposi village, on the south part of the island.

Damage to buildings on Posiposi Rao Island following the 19 Novenmber 2017 Earthquake. Earthquake Report.

Posiposi Rao lies at the northern end of the Halmahera Islands chain, a volcanic arc formed where one tectonic plate is being subducted beneath another, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. However the Halmahera Islands are unusual in that they lie on a double subduction zone. The underlying plate, a northeaster extension of the Molucca Sea Plate, is being overridden form the Philippine Plate from the east and the Eurasian Plate from the west. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

 Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

The approximate location of the 19 November 2017 Posiposi Rao Earthquake. USGS.

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Eruptions on Mount Ibu, Halmahera, Indonesia.

The Darwin Volcanic Ash Advisory Center has reported eruptions on Mount Ibu, a stratovolcano (cone-shaped volcano made up of layers of volcanic ash and lava) on the northwest coast of Halmahera Island, Indonesia, on Thursday 24 and Monday 28 August 2017. Both eruptions were identified from ash plumes that rose 1.5-1.8 km above the summit of the 1325 m volcano and drifted to the west.

The approximate location of Mount Ibu. Google Maps.

The Halmahera Islands arc a volcanic arc; formed where one tectonic plate is being subducted beneath another, with the underlying plate being melted by the heat of the Earth's interior, and lighter minerals bubbling up through the overlying plate to form volcanoes. However the Halmahera Islands are unusual in that they lie on a double subduction zone. The underlying plate, a northeaster extension of the Molucca Sea Plate, is being overridden form the Philippine Plate from the east and the Eurasian Plate from the west. The Halmahera volcanoes are located where the Philippine Plate is overriding the Molucca Sea Plate; to the west the Sangihe Islands lie where the Molucca Sea Plate is being overridden by the Eurasian Plate.

 Diagrammatic representation of the subduction zones beneath Halmahera (middle), plus the Philippines (top) and Sulawesi (bottom), with the Eurasian Plate to the left, the Molucca Sea Plate in the middle, and the Philippine Plate to the right.  Hall & Wilson (2000).

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